Evaluating the Geometric Design Consistency and Road Safety on Two-lane Single Carriageways Using Operating Speed Criteria

Abstract

This work focuses on two-lane single carriageways that contain
sections, which make transition from one geometric feature to
another unsafe, and thereby resulting in driving errors that may
eventually lead to driving off course and accidents. The two-lane
single carriageway selected for the study was the EkiadolorOlumoye-Uhen road, a rural highway in Edo State, Nigeria.
Alignment data such as curve radius, length of curve, beginning and
end point of curve, as well as vertical slope, were obtained from
satellite imageries using Geographic Information System (GIS);
while the operating speed reduction (∆V85) between tangents and
curves was estimated at various sections of the selected route. These
data were used as input parameters in generating an Accident
Prediction Model. The model was generated using the Generalized
Linear Regression Modelling (GzLM) approach. The results
obtained from the study showed that the curves between sections 11.4
– 11.9km, 21.5 – 22.0km and 24.0 – 24.5km, fell slightly short of the
criteria of a good design and therefore required warning signs to be
placed before the transitions; whereas the curves between sections
16.8 – 17.4km and 26.6 – 27.8km, fell very short of the criteria of a
good design, and were classed as poorly designed.